Been researching alot about cams and have learned a lot, but still confused on one small (or maybe not) part. What exactly is the difference between a cam ground in with * of advance vs. none?

For example, say you have two cams both exactly the same specs:

224/230 cam .60x .60x lift

but one is a 112+2 LSA with 2* advance ground in = 110 ICL

and the others is a 110+0 LSA with 0* advance ground in = 110 ICL

Both have 110 ICL in the end, but one achieves it through ground in advance while the other is straight up. Is there really a difference in these, or are they basically the same?

 

Advance and retard basically moves the torque band up and down the RPM range. With adjustable timing sets you can achieve the same thing as having a cam with advance/retard ground in. Seems that most cams have some advance ground in. The play in the timing set and chain can essentially retard the cam a couple degrees as well.

http://www.lunatipower.com/Tech/Cams/CamSpecTerms.aspx

 

LSA=lobe seperation angle, and ICL=intake centerline. The ICL and ECL (exhaust centerline) added together divided by 2 give you the LSA. So in a nutshell, yes both the centerlines play a pivotal role on the powerband

 

LSA affects overlap. ICL/ECL don't. They simply determine where the IVC/IVO and EVO/EVC events happen in relation to peak lift at TDC. For the purposes of cam tuning, most look at the IVC/EVO operations as most important for a street car. The more advance you have, the later the EVO happens and the earlier the IVC happens. This creates torque but hurts some of the efficiency of the 4-stroke cycle because you hang open the exhaust valve in an attempt to scavenge the intake air charge into the cylinder. With the stock LS1's weak exhaust port and F-body's weak exhaust, this is actually a good crutch.

By closing the intake sooner and opening the exhaust later, you create more compression and torque. The alternative is to set the LSA tighter with no advance and have more exhaust duration. It would have a similar effect on the valve events at the cost of a lot more overlap during the critical phase of EVO and IVC to create that overlap and scavenge phase.

Therefore, the reason you might have a cam at 112+2 vs 110+0 would be streetability due to a lower overlap (which hurts power production, but create an easier to drive car).

Best way I can show it is a 232/236 cam on a 112+2 vs a 232/244 on a 110+0. Look at the VEs (nearly the same except for EVC):

Intake Duration - ID 232 232
Exhaust Duration - ED 236 244
Lobe Center Angle - LCA (also known as LSA) 112 110
Intake Centerline - ICL 110 110


Intake Valve opens - IVO 6 6
Intake Valve closes - IVC 46 46
Exhaust Valve Opens - EVO 52 52
Exhaust Valve Closes - EVC 4 12
Exhaust Centerline - ECL 114 110
Overlap 10 18

 

Jake basically hit the nail on the head here, but I would like to address a few points.

ICL and ECL can actually affect overlap, not the overall overlap figure itself at any given lift point, but where that overlap period starts and stops. The overlap period begins when the intake valve is opening and while the exhaust valve is closing. By moving the ICL/ECL you can adjust when it occurs in relation to crank angle. I've found you can open the intake and close the exhaust valve later for a given amount of overlap and not hurt drivability as much as you would with closing the exhaust valve earlier and opening the intake valve earlier. For this reason I like to center most of my N/A IVO and EVC overlap events unless it's a single plane short intake runner type deal that needs a lot of intake scanvenging.

That last part goes with the next thing I wanted to point out that Jake said, I do think IVC/EVO are important, but IVO and EVC are also just as important to me because again it changes where the overlap period starts and stops. Also the more ICL advance you have the earlier the exhaust valve opens not the later it opens. Advancing advances all the events. Opening the exhaust valve doesn't have any effect on when the overlap phase happens, but it does affect the total amount of overlap in relation to how large or how small that figure is. The exhaust valve close event is what coincides with scavenging the intake port not the EVO event. Advancing the cam will pull the peak torque/horsepower rpm's down but likely reduce peak numbers at the same time for both torque and horsepower, but increase under the curve and average power. Opening the exhaust valve earlier will blow down the cylinder sooner and at low rpm this is inefficient because it loses energy necessary to make more torque at low rpms. Not until higher rpm's does blowing down the cylinder sooner start to show gains, but it does seem to create more average power if conincided right with other events and overlap.

 

I was close. It was late. Wine etc.

 

You've been cut off officially from your bottle Jake!

 

224/230 112+2 and 224/230 110+0 are two different cam specs (different LSA)...

yes, they both have the same ICL (110), but their ECL is different (114 vs 110).

The 112+2 cam is simply a 112 cam advanced 2 degrees (the whole cam).